The present disclosure relates to a method for operating a powertrain of a motor vehicle in order to improve the driveability of the vehicle. The present disclosure may be applied in heavy duty vehicles, such as trucks, buses and construction equipment. Although the disclosure will be described with respect to a heavy duty vehicle, the disclosure is not restricted to this particular use but may also be used in other vehicles such as e.g. passenger cars.
Vehicles equipped with either manual or automatic transmissions using friction clutch may during the engagement of the friction clutch at vehicle take-off experience a phenomenon often referred to as clutch judder. Clutch judder appears at vehicle system oscillations at approximately 5 to 20 Hz. Clutch judder may originate from various sources and is influenced by many components of the vehicle, but the fundamental cause of the occurrence of clutch Judder is that oscillations occurring during the engagement of the friction clutch correspond to the resonance frequency of the currently engaged gear. Clutch judder significantly affects the driveability and the driver comfort of the vehicle and if the clutch judder is sever it may even make concerned vehicle undrivable. Also, reoccurring, sever clutch judder may be harmful the vehicle.
Today most solutions to clutch judder related problems are focusing on suppressing the oscillations by e.g. using damping materials. However, the damping effect of using materials often decay over time, thus such solutions are only temporarily.
US 2005/0189192 discloses a method for reducing juddering vibrations. According to US 2005/1089192 the judder is detected by analysing rotational speed of e.g. a transmission input shaft. The judder is subsequently rectified by automatic adjustment of a device being disposed in the drivetrain, or coupled thereto, in such a manner that a rotary parameter, such as torque or speed, which is assigned to a drivetrain component, is modified. However, in US 2005/0189192, and in other related prior art, no measures are taken in order to identify the origin of the clutch judder. Thus, no preventive or long term lasting countermeasures are performed. The countermeasures proposed are often quite general and not that effective.
Thus, there is a need of further improvements.
It is desirable to provide a method for improving the driveability of a vehicle it is also desirable to improve the durability of the vehicle.
During engagement of a friction clutch at take-off, various sources, which are dependent on various vehicle configurations, may cause oscillations in the vehicle powertrain. If such oscillations coincide with the resonance frequency of the powertrain of the vehicle, at the current gear, this may cause clutch judder. Clutch judder has strong negative impact on the driveability of the vehicle, which may be dangerous, and may also, especially if occurring over a long period of time, be harmful for the vehicle and/or vehicle components.
A method for operating a powertrain of a motor vehicle at take-off thus during the engagement of a friction clutch, will be presented. The powertrain comprises an internal combustion engine, a transmission and the friction clutch arranged there between in order to control a power flow between the engine and the transmission.
The method comprises the steps of:
detecting clutch judder, wherein the detection of clutch judder is based on at least one predetermined vehicle variable,
analysing clutch judder characteristics by evaluating the at least one predetermined vehicle variable in order to:
determining a type of clutch judder,
selecting a judder countermeasure, based on determined type of clutch judder, from a number of predetermined judder countermeasures, and
executing selected judder countermeasure.
The clutch judder characteristics are the variation in rotational speed of e.g. an input shaft over time caused by the clutch judder. The present disclosure has the effect that by continuously detecting clutch judder, and determining the type of clutch judder, the judder countermeasures, hereafter referred to as simply countermeasures, taken may be dependent on the source of the clutch judder. Thereby the most efficient countermeasure may be executed and clutch judder may be avoided in the future.
Clutch judder may be detected by analysing when there is a reoccurring irregularity in at least one predetermined vehicle variable, and wherein said irregularity exceeds a predetermined threshold value. The threshold value may e.g., be set according to when the clutch judder is experienced as annoying by a driver or when there is an imminent risk that the judder may cause premature wear of the powertrain if it persists over time. The threshold value is preferably also set in respect to what predetermined vehicle variable that is analysed. If clutch judder is detected the type of clutch judder may be determined by analysing the clutch judder characteristics wherein that most suitable countermeasure may be executed.
The method, including all the method steps, is run by an Electronic Control Unit (ECU) of the vehicle and is controlled by the software of the ECU. When referring to that the method is performed by an ECU this is not limited to that the method is performed by one single control unit The method may be performed by a distributed control unit comprising numerous interacting control units and local controllers of the vehicle. This is also referred to as the computer of the vehicle. A computer is by definition a programmable electronic device that can retrieve, store, process and redistribute information, thus the same operations as the control unit, being a single component or a network of interacting components, is provided to perform.
Further, In an exemplary embodiment the method may be run continuously during vehicle take-off, meaning that the method step of detecting, and possibly also the following method steps, are carried out as the friction clutch is being engaged. An exemplary embodiment of the method may be adaptive. This means that when clutch judder is detected, which triggers that a clutch judder countermeasure is executed, the specific vehicle operating conditions are also logged wherein next time the vehicle is about to operate at similar operating conditions countermeasures may be performed in advance or operating at the specific operating conditions where clutch judder previously has occurred may be avoided.
According to an exemplary embodiment of the present disclosure the one predetermined vehicle variable is a rotational speed of a power transferring part in the powertrain. According to another exemplary embodiment the predetermined vehicle variable may be vehicle acceleration or oscillations of some other part of the powertrain or the vehicle.
According to another exemplary embodiment of the present invention the predetermined vehicle variable used in the method step of detecting clutch judder may be acceleration and/or inclination Input provided by e.g. an acceleration sensing means or inclination sensing means. However, even if acceleration and/or inclination is used in the method step of detecting clutch judder a predetermined vehicle variable such as rotational speed of a power transferring part the powertrain may be used in the subsequent method steps of analysing clutch judder and determining type of clutch judder.
According to exemplary embodiment of the disclosure this power transferring part of the powertrain is an input shaft of the transmission. Examples of other power transferring parts of the powertrain for which the rotational speed may be analysed is any gear wheel, a main, counter or an output shaft, a drive axle or the wheels. If the rotational speed of e.g. the input shaft temporarily decreases each time the rotating shaft is in a particular position, this may be an Indication of the occurrence of clutch judder. It is possible to analyse the rotational speed of either one of the moving parts which are involved in the transfer of power from the engine to the wheels. However, depending on for which moving part of the powertrain the rotational speed is analysed compensation for difference in gear ratio in relation to the input shaft may have to be applied. Thus, as long as the rotational speed of a part involved in the transfer of power from the engine to the transmission can be directly coupled to rotational speed of the input shaft, and the gear ratio relation to the input shaft can be determined, that part can be analysed in order to detect clutch judder. For a multi clutch transmission a moving part which is involved irrespectively of which of the clutches that are engaged, or the speed of a moving component of each clutch, may be used when analysing the rotational speed. Advantageously the speed of one power transferring part, such as e.g. a shaft of the transmission, which is provided with a rotational speed sensor used for additional purposes, such as OBD, On Board Diagnostics etc., is used.
The power transferring part in the powertrain may preferably be one of the shafts of the transmission, e.g., the main, counter, output or input shaft.
According to yet an exemplary embodiment of the present disclosure the determination of a type of clutch judder is based on a clutch judder frequency. By assessing the clutch judder frequency in relation to at least one predetermined vehicle variable it is possible to identify the origin of the clutch judder and thus determine the type of clutch judder. Clutch judder frequency is defined as the frequency of the judder and is further discussed in relation to FIG. 3a-3d. 
The most suitable countermeasure in order to rectify respective type of clutch judder is dependent on the type of clutch judder, in the following disclosure a few different types of clutch judder, with exemplary countermeasures suitable for respective type of clutch judder, will be disclosed.
According to one example the method step of determining type of clutch judder further comprises the method steps of:
comparing the clutch judder frequency with an engine frequency, and
evaluating if the clutch judder frequency matches the engine frequency or matches half the engine frequency.
In the subsequent method step it is determined that if the clutch judder frequency matches the engine frequency, or half the engine frequency, at the current gear the clutch judder Is engine related. If the judder only occurs on certain gears this may also be an indication of that the clutch judder is engine related.
If the clutch judder frequency matches the engine rotational speed frequency, thus if the frequency derived from rpm (revolutions per minute) of the engine is equal to the resonance frequency of the current gear, it is possible that the clutch judder is related to hardware participating; in each revolution of the engine, e.g. the clutch judder may be related to the rotation of the crankshaft. If the clutch judder frequency matches half the engine frequency it is instead possible that the clutch judder is related to one single cylinder. Each time that single cylinder ignites, which is once per every second revolution of the engine, something occurs which in some way induce clutch judder. This may e.g. be due to misfire of said cylinder or that more or less fuel is injected into that cylinder than into other cylinders.
If it is determined that the clutch judder is related to the engine, exemplary countermeasures may be that the ECU automatically increases the rotational speed of the engine when starting on a gear where clutch judder has been detected or, if possible, avoid starting such gears completely. A predetermined maximum level of starting rotational speed may be necessary in order to protect the clutch and related components and to not deteriorate the driver comfort.
As will be discussed more in detail later, the friction clutch also comprises a pressure plate and the powertrain comprises a flywheel. According to a second example the method step of determining a type of clutch judder comprises the steps of:
comparing the clutch judder frequency with a rotational speed difference frequency which is dependent on a rotational speed difference between the rotational speed of a power transferring part in the powertrain and the rotational speed of the engine, and
evaluating if the clutch judder frequency matches the rotational speed difference frequency.
The power transferring part may e.g. be the input shaft or any other shaft currently involved in the transferring of power. Depending on what power transferring part that is used as reference to the rotational speed of the engine when determining the rotational speed difference frequency it may be necessary to compensate for difference in gear ratio between the power transferring part and the input shaft. Thus, the rotational speed difference frequency is defined as the frequency derived from the difference in rotational speed between the rotational speed of the engine and the rotational speed of the input shaft. If the rotational speed of an other power transferring part than the input shaft is used in order to determine the rotational speed difference frequency a difference in gear ratio between power transferring part and the input shaft may have to be applied.
In the method step where the type of clutch judder is determined it Is determined that if the clutch judder frequency matches the rotational speed difference frequency the clutch judder is related to the angular tolerance between the pressure plate and the flywheel of the clutch of the vehicle. When a friction clutch, which will be described in detail in relation to FIGS. 4a and 4b, is engaged during vehicle take-off, e.g. by that a driver releases the clutch, the pressure plate of a releasing means is configured to act on a friction plate, such that the friction plate engage with a flywheel of a crankshaft. The friction plate is connected to an input shaft and by engaging the flywheel of the crankshaft with the friction plate of the input shaft the input shaft and the crankshaft are engaged such that rotational power (torque) can be transferred from the crankshaft to the input shaft. Clutch judder related to the angular tolerance between the pressure plate and the flywheel may e.g. be caused by machining variations or displacement due to external force. If so, this causes the friction plate and the flywheel to unintentionally engage, or engage to a higher extent than what is expected, at a certain point during rotation of the pressure plate. This may cause oscillations of the powertrain. If these oscillations match the resonance frequency of the current gear this may cause clutch judder.
If the clutch judder frequency matches the rotational speed difference frequency it can be determined that the clutch judder may be related to the angular tolerance between the pressure plate and the flywheel. It may thereby be possible to minimize the clutch judder problem by avoiding take-off on the gear on which the clutch judder appears, which at least will reduce the number of times the driver is subjected to clutch judder. When starting on a gear where clutch judder occurs cannot be avoided the problem can be minimized by passing the critical rpm as quickly as possible.
Further, the friction clutch comprises a release bearing and a diaphragm spring, which also will be disclosed more in detail later. According to a third example the method step of determining a type of clutch judder comprises the steps of:
comparing the clutch judder frequency with the rotational speed of a power transferring part in the powertrain, and
evaluating if the clutch judder frequency matches the rotational speed of the power transferring part in the powertrain.
In the subsequent method step, where the type of clutch judder is determined, it is determined that if the clutch judder frequency matches the rotational speed of the power transferring part in the powertrain the clutch judder is related to the angular tolerance between the release bearing and the diaphragm spring. The economically realizable tolerances may during certain conditions, such as e.g. if the current vehicle as such is particularly sensitive to clutch judder, not be sufficient. Another reason may be that a number of related tolerance intervals interact in an unfavorable way. A deficiency in the angular tolerance between the release bearing and the diaphragm spring may result in that the flywheel and the pressure plate are not parallel. This may also be caused by errors when manufacturing or assembling components. Not parallel flywheel and pressure plate may result in that the friction plate is not evenly engaged to the flywheel when the pressure plate acts on the friction plate during engagement of the clutch. Uneven engagement of the friction plate and the flywheel may cause oscillations in the powertrain, and if these oscillations correspond to the resonance frequency of the current gear this may cause clutch judder.
Exemplary countermeasures if the clutch judder frequency matches the rotational speed of the power transferring part in the powertrain are the same as if the clutch judder frequency matches the rotational speed difference frequency, i.e. avoiding take-off on concerned gear and secondly by passing the critical rpm as quickly as possible.
In order to determine that clutch judder origin either from the angular tolerance between a pressure plate and a flywheel or from the angular tolerance between the release bearing and the diaphragm spring it may also be Important to analyse at what rpm and at what time from vehicle take-off the clutch judder start and at what rpm and at what time from vehicle take-off the clutch judder stops. This may also be used as an indication when determining type of clutch judder.
According to a fourth example, subsequent to the engagement of the friction clutch of the powertrain has been initiated, the method step of determining a type of clutch judder comprises the method sub steps of:
evaluating whether, during the engagement of the friction clutch, the highest rotational speed acceleration of a power transferring part in the powertrain started from zero rotational speed, and
evaluating whether the clutch judder is engine related.
In the following step here the type of clutch judder is determined it can further be concluded that;
if it is determined that the clutch judder was not engine related, and
if the highest rotational speed acceleration of the analysed power transferring part in the powertrain started at zero rotational speed
the clutch judder is related to the engagement of the friction clutch.
If it is determined that the clutch judder was related to the engagement of the friction clutch this can be avoided during subsequent vehicle take-offs by minimizing the torque peak. This can be achieved by adjusting the clutch starting position or by simply reducing the speed at which the clutch is engaged, thus increase the time during which the clutch is engaged. Normally, engagement related clutch Judder is damped out with time.
Thus, the selected clutch judder countermeasure may be selected from a group of judder countermeasures comprising:
increasing rotational speed of the engine during a take-up period,
avoiding starting on specific gears,
adjusting the rotational speed at which the clutch is engaged,
adjusting clutch starting position, and/or
passing critical engine rotational speeds
wherein selected countermeasure is dependent on the determined type of clutch judder and what the origin of respective type of judder is.
Many vehicles of today are equipped with an acceleration sensing means and/or an inclination sensing means configured to measure acceleration over time, such as an accelerometer or like. Assessing the clutch judder frequency in relation to at least one predetermined vehicle variable is sufficient in order to detect and classify clutch judder. However, just by assessing clutch judder frequency in relation to at least one predetermined vehicle variable It may not be possible to assess how sever the clutch judder is. Thus, for vehicles equipped with an acceleration sensing means and/or inclination sensing means, when, clutch judder is detected the method of the present disclosure may further comprises the steps of;
collecting information from the acceleration sensing means and/or the inclination sensing means of the vehicle,
combining information from the acceleration sensing means and/or inclination sensing means with clutch judder characteristics, wherein the clutch judder characteristics are given by evaluating the clutch judder frequency over time, and
evaluating the criticality of the clutch judder.
By evaluating the criticality, or how sever the clutch judder is, it is possible to identify operation modes where clutch judder may be present but where it may not, by assessing the operation mode as a whole, be noticeable from a driveability or durability aspect. Also, the criticality of the clutch judder may determine what countermeasure that is suitable at respective occasion.
The present disclosure also comprises a computer program comprising program code means for performing the steps of any exemplary embodiments of the method of the present disclosure when said program is run on a computer such as an ECU. The present disclosure also comprises a computer readable medium carrying a computer program comprising program code means for performing the steps of any embodiment of the method when said program product is run on a computer such as an ECU. Further, the present disclosure comprises an ECU in accordance to what previously has been disclosed for controlling any embodiment of the method of operating a powertrain, wherein the ECU is configured to perform the steps of any embodiment of the method.
Further effects and advantageous features of the disclosure are disclosed in the following description and in the dependent claims.